With the advent of high power, high performance electric drive technology, transportation vehicles are increasingly being moved from the combustion engine platform to electric propulsion systems. Not only electric vehicles are more power efficient and robust due to their lesser number of internal components, but also they produce little or no environmentally harmful emissions associated with the ignition of fossil fuels in combustion engines.
High power battery packs are the key components for the successful implementation of electric drive technology in transportation vehicles. The battery pack is the main source of power for the pure electric propulsion system and comprises a plurality of series or parallel-connected cells. Initially, battery packs including a number of acid-lead cells were employed. The acid-lead cells were electrically coupled in series to one another to provide sufficient power for the electrical drive mechanism of the early electric vehicles. However, these early battery packs were quite bulky and heavy, and a short life cycle. Moreover, the acid-lead battery packs had a short cycle life, long charge time, and did not provide sufficient battery power over a long range.
In order to overcome some of these limitations, the manufacturers of battery packs have realized that batteries using the nickel-metal hydride cells or lithium-ion cells were lighter and less bulky, with a longer cycle life, faster charging and provided higher output power for longer distances. Accordingly, the nickel-metal hydride or lithium-ion battery packs have become the storage media of choice for high power applications such as electric drive vehicles.
In spite of the enormous success of the nickel-metal hydride battery packs, these devices suffer from the drawback that they are typically custom-designed for a specific application, having regard to the mechanical, thermal and electrical design constraints that are specific to the application. As a result, these battery packs are not interchangeable and cannot be readily integrated in other vehicles or high power applications.
Another major drawback of the existing battery packs is that the service life of the battery pack is typically shorter than other components of the vehicle. Due to high current drainage and high thermal operating conditions, it is not uncommon for the battery pack to fail and be replaced. The vehicle system controller is a component separate from the battery pack itself and outlasts the battery pack. As a result, every time a battery pack is replaced, the vehicle system controller must be calibrated or even replaced so as to correspond with the specifications of the new battery pack. Moreover, although the failure of the battery pack may be due to non-ideal performance or breakdown of one or a few individual battery cells within the battery pack, often the entire battery pack is to be replaced, as it is not possible to diagnose and manage the battery cells individually during operation.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.